Builder API to configure thread pool size.

Author: mstyura

objectbox-java/src/main/java/io/objectbox/BoxStore.java

@@ -227,7 +227,7 @@ public static boolean isSyncServerAvailable() {
     private final int[] allEntityTypeIds;
     private final Map<Class<?>, Box<?>> boxes = new ConcurrentHashMap<>();
     private final Set<Transaction> transactions = Collections.newSetFromMap(new WeakHashMap<>());
-    private final ExecutorService threadPool = new ObjectBoxThreadPool(this);
+    private final ExecutorService threadPool;
     private final ObjectClassPublisher objectClassPublisher;
     final boolean debugTxRead;
     final boolean debugTxWrite;
@@ -257,6 +257,11 @@ public static boolean isSyncServerAvailable() {
     private SyncClient syncClient;
 
     BoxStore(BoxStoreBuilder builder) {
+        threadPool = new ObjectBoxThreadPool(
+            this,
+            builder.threadPoolCoreSize,
+            builder.threadPoolMaxSize,
+            builder.threadPoolThreadKeepAliveSeconds);
         context = builder.context;
         relinker = builder.relinker;
         NativeLibraryLoader.ensureLoaded();

objectbox-java/src/main/java/io/objectbox/BoxStoreBuilder.java

@@ -91,6 +91,12 @@ public class BoxStoreBuilder {
 
     int fileMode;
 
+    int threadPoolCoreSize = 0;
+
+    int threadPoolMaxSize = Integer.MAX_VALUE;
+
+    int threadPoolThreadKeepAliveSeconds = 20;
+
     int maxReaders;
     boolean noReaderThreadLocals;
 
@@ -288,6 +294,35 @@ public BoxStoreBuilder fileMode(int mode) {
         return this;
     }
 
+    /**
+     * Sets the core size of thread pool used by BoxStore. The default is 0.
+     * You may want to change it along with {@link #threadPoolThreadKeepAliveSeconds}
+     * to make fresh threads creation not very often.
+     */
+    public BoxStoreBuilder threadPoolCoreSize(int threadPoolCoreSize) {
+        this.threadPoolCoreSize = threadPoolCoreSize;
+        return this;
+    }
+
+    /**
+     * Sets the max number of threads allowed in thread pool used by BoxStore. 
+     * The default is {@link Integer#MAX_VALUE}.
+     * You may want to limit max thread pool size to avoid OOM when thread
+     * count become too large for device.
+     */
+    public BoxStoreBuilder threadPoolMaxSize(int threadPoolMaxSize) {
+        this.threadPoolMaxSize = threadPoolMaxSize;
+        return this;
+    }
+
+    /**
+     * Sets the number of seconds thread kan stay idle in thread pool before termination.
+     */
+    public BoxStoreBuilder threadPoolThreadKeepAliveSeconds(int threadPoolThreadKeepAliveSeconds) {
+        this.threadPoolThreadKeepAliveSeconds = threadPoolThreadKeepAliveSeconds;
+        return this;
+    }
+
     /**
      * Sets the maximum number of concurrent readers. For most applications, the default is fine (~ 126 readers).
      * <p>

objectbox-java/src/main/java/io/objectbox/internal/ObjectBoxThreadPool.java

@@ -39,8 +39,8 @@
 public class ObjectBoxThreadPool extends ThreadPoolExecutor {
     private final BoxStore boxStore;
 
-    public ObjectBoxThreadPool(BoxStore boxStore) {
-        super(0, Integer.MAX_VALUE, 20L, TimeUnit.SECONDS, new SynchronousQueue<>(),
+    public ObjectBoxThreadPool(BoxStore boxStore, int corePoolSize, int maximumPoolSize, int threadKeepAliveSeconds) {
+        super(corePoolSize, maximumPoolSize, threadKeepAliveSeconds, TimeUnit.SECONDS, new SynchronousQueue<>(),
                 new ObjectBoxThreadFactory());
         this.boxStore = boxStore;
     }